Solar powered light source or the like



July 7, 1959 M. E. PARAQISE SOLAR POWERED LIGHT SOURCE OR THE LIKE IOriginal Filed Oct. 3, 1955 LAR CELL v FIG. 1

IN VEN TOR.

5o| MAURICE E. PARADISE HIS ATTORNEY FIG. 5

United States Patent 2,894,173 SOLAR POWERED LIGHT SOURCE OR THE LIKEDivided and this application September 22, 1958, Serial No. 762,320

3 Claims. (Cl. 315-86) This application is a division of co-pendingapplication Serial No. 538,229, filed on October 3, 1955, in the name ofthe same inventor and assigned to the same assignee.

This invention is related to devices which utilize the phenomenon ofphoton emission from the sun to develop and store electrical energy forsubsequent usage to power a source of light in the visible wave lengthregion, and more particularly to a new and improved solar powered devicewhich produces in the daytime or nighttime intermittent vissible flashesof light, this device being characterized by long-time reliability andextreme portability.

Of current interest is the development of the solar cell, as it iscalled, that is, means responsive to impinging photon emanations fromthe sun or other source for developing a corresponding D.C. potential-aphoto-electric transducer. Photo sensitive semiconductors, whichgenerally constitute the structure of solar cells, are either pointcontact devices or p-n junction semiconductors. The junction may beeither of the grown, the alloyed, or the diffused variety. P-n junctionsemiconductors have thus far proven to be the most satisfactory forincorporation in solar cells. The basic principle of operation is thatphotons generated by the solar source are permitted to impinge upon ap-n junction semiconductor in the region of the junction, in order toproduce hole-electron pairs. It is well known that it is not necessaryfor the hole-electron pairs to be generated in the junction itself toproduce a current, but merely in such regions that there is a goodprobability of the carriers diffusing to the junction. With presentefiiciencies it has been found that several p-n junction semiconductordevices must be series-connected in order to develop a practicable DC.voltage. Lens systems are frequently employed with a battery of solarcells in order to assure a maximum of photon impingement upon each cellfor a given ambient light intensity. To be operated satisfactorily,solar cells are hermetically sealed, and, by such sealing the solar celllife becomes almost indefinite. Batteries comprising small numbers ofsolar cells have been found to be very adequate for small loads. Hence,any light source to be powered by such cells must exhibit a low powerconsumption. In the present invention the light source is a simplerelaxation oscillator employing one or more neon tubes. This is thedirection which the present invention pursues.

Therefore, it is an object of the present invention to provide a new anduseful intermittent light source which is supplied electric power by oneor more solar cells.

It is a further object of the present invention to provide a new anduseful light source having a solar cell power supply in which the lightsource itself is turned olf automatically during the day, and in whichthe light source resumes its intermittent operation automatically atnight.

It is a further object of the present invention to provide a novelcircuit in which a relatively low voltage solar cell is adapted forpowering high voltage inert gas filled tubes.

According to the present invention, a solar cell or a battery of suchcells is coupled in charging relationship across a secondary batterypower supply associated with an inert gas tube relaxation oscillator.Relaxation tube oscillators in the various embodiments generate either alow voltage or a high voltage output for application .to the gas tube.If desired, a resistor may be included in the solar cell circuit tosupply a bias voltage which cuts 01f the gas tube during the day or atany other time when the solar cell or solar battery is generating apotential.

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The presentinvention, both as to its organization and manner of operation, togetherwith further objects and advantages theerof, may best be understood byreference to the following description, taken in connection with theaccompanying drawings, in which,

Figure 1 is a schematic diagram of a solar powered light sourceaccording to the present invention.

Figure 2 is a schematic diagram of a modification of the circuit ofFigure 1 in which a grid-controlled, inert gas filled tube is employed.

Figure 3 is an additional embodiment of the present invention in which,as a result of high current surges through an inductive reactance, highvoltage is supplied the associated gas tube.

Figures 4A, 4B, and 4C are diagrams relating to the characteristic ofthe double-based diode employed in the circuitry of Figure 3.

Figure 5 is a modification of the high voltage relaxation tubeoscillator circuit of Figure 3.

In Figure 1, solar cell unit 10 (consisting of one or more cells andhereinafter referred to as solar cell") is coupled across battery 11,which in turn is coupled through an R-C integrating circuit consistingof resistor 12 and capacitor 13 to inert gas filled tube 14. Solar cell10 is a photovoltaic device and preferably exhibits a generally higherterminal voltage than battery 11 and may comprise any one of the severaltypes of solar cells being developed at the present time, though a solarbattery made up of a plurality of diffused junction semiconductors wouldbe preferable. There are many types of secondary batteries which may beemployed as battery 11 in Figure l, as for example the Gouldhermetically sealed nickel-cadmium storage cell, which may be rechargedan indefinite number of times and has an extended life. If desired, bothsolar cell 10 and battery 11 may be enclosed in a single, hermeticallysealed casing. Or, if desired, the entire circuitry of Figure 1 may beincluded in a single hermetically sealed container. Tube 14 may be aconventional neon tube or other type of cold cathode, gas tube.

The circuit of Figure l operates as follows. The combination of battery11, resistor 12, capacitor 13, and tube 14 constitutes an elementaryrelaxation oscillator the operation of which is well known. The momentthat battery voltage is applied to the circuit, capacitor 13 chargesthrough resistor 12 until the ionization potential of tube 14 isreached, at which time tube 14 fires permitting capacitor 13 todischarge therethrough. Hence the voltage signal impressed across tube14 will be one of intermittent peak amplitude. If desired, a currentlimiting resistor may be included in the circuit of tube 14. Theinclusion of solar cell 10 in the circuit of Fig ure 1 adds novelty tothe circuit in that during the day photons impinging upon the solarbattery or cell 10 will generate current to charge battery 11. At nightin the absence of artificial light solar cell 10 becomes inoperative, sofar as the generation of electrical energy is concerned, but would drawa slight current from battery 11. This current would be extremely smallbecause of the high backresistance of solar cell 10. If desired, a diodemay be appropriately placed in the solar cell cir cuit to preventbattery 11 from discharging through solar cell during the night hours.The inclusion of diode 200 in the circuit of Figure 2 exemplifies thisfeature which is equally adaptable to the circuit of Figure l.

The circuit of Figure 2 is substantially the same as that of Figure 1with the exception of the inclusion of diode 200 inthe solar cellcircuit, the inclusion of bias resistor 201, and a substitution oftriode glow tube 202 for tube 14 in Figure 1.

The circuit of Figure 2 operates as follows. As is hereinbeforeexplained, in the absence of artificial light current flows in the solarcell circuit only during daylight hours, the back-resistance of diode200 and of solar cel 204, itself, preventing discharge of battery 203through cell 204. Hence, in the daytime hours, the bias voltagedeveloped across resistor 201 is applied to control electrode 205 whichaccordingly renders tube 202 non-conductive during the day, whenoperation of the light is not necessary. This biasing feature willfurther serve to enhance the long life of battery 203. When nightarrives, current ceases to flow through the solar cell circuit and thebias voltage is removed from control electrode 204 of tube 202 allowingtube 202 to conduct intermittently, the intervals between conductionbeing determined by the R-C time constant of the circuit. Hence, thecircuit of Figure 2 will be operative only at nighttime or under lowambient light conditions, which is to be desired. I

In Figure 3, solar cell 300 is coupled across battery 301 which is inturn coupled across the bases of double based diode 302. Resistor 303 iscoupled between the emitter and one of the base terminals of diode 302.The emitter is also coupled through capacitor 304 and primary winding305 of transformer 306 to the opposite base of double-based diode 302.Secondary winding 307 of transformer 306 is coupled through currentlimiting resistor 308 to the opposite terminals of gas tube 309.

The circuit shown in Figure 3 operates as follows. Again, solar cell 300will supply current to the circuit only when photons are impinging uponthe sensitive surfaces thereof. In order to understand the operation ofthis circuit, one must recall the theory of operation of double-baseddiodes. For this reason, attention is direct'ed to the characteristiccurves of double-based diodes, as indicated in Figures 4A, 4B, and 40.Consider the n acceptor portion of double-based diode 302 to be oflength L and that the p emitter portion of thedoublebased diode liessubstantially half-way between the extremities of the n portion. Then byvirtue of the imposition of a voltage across the bases of double-baseddiode 302 by battery 301 there will exist in the 11 acceptor portion apotential gradient which will be substantially linear, as is indicatedin the diagram of Figure 4A. Thus, considering the applied batteryvoltage to be of magnitude E, the potential adjacent the center of the pemitter region will be E/ 2. Now, upon applying battery voltage E to thecircuit of Figure 3, capacitor 304 will commence to charge through theparallel combination of resistor 303 and the back-resistance of theupper portion of double-based diode 302. The situation described inFigure 4A is not stable, however, even considering for the moment thatthe voltage across capacitor 304 were held constant, since, as the holesdifiuse into the n acceptor portion from the p emitter portion, theywill drift toward the negative end of the acceptor portion under theinfluence of the transverse electric field in that portion. The presenceof the holes lowers the resistivity of this portion so that thepotential along the acceptor portion redistributes itself in a wayrepresented by Figure 4B. It is to be noticed that the 13/2 that morethan half of the p portion is biased as an emitter. Soon afterwards,substantially all of the p portion will be biased as an emitter, as isindicated by the continued heightening of the E/2 point on the curve inFigure 4C. The p emitter portion, now being fully biased as an emitter,allows capacitor 304 to discharge suddenly through primary winding 305.This current surge in primary winding 305 of transformer 306 appears asa voltage pulse in the secondary winding circuit which fires neon tube309. Current limiting resistor 308 reduces the current flow to the tubeso as to prevent damage thereto. The discharge of capacitor 304 throughthe double-based diode 302 restores the emitter (L/ 2 region) potentialto a very low value, thus rendering diode 302 substantiallynon-conducting. As soon as this non-conductive state is attained, thecapacitor 304 again recharges through resistor 303 and theback-resistance of the upper portion of double-based diode 302, and thecycle is' resumed. Hence, the objective in view, namely that of derivingfrom a low voltage source a high volt age to fire tube 309 is achieved.

It will be seen that, in essence, double-based diode 302 accomplishesthe same result as that of a conventional thyratron; that is, by virtueof triggered high current surges, a large output voltage may be obtainedfrom a relatively small voltage source. There are in recent developmentmany types of semiconductor devices which may be employed in lieu ofdouble-based diode 302. Indeed, articles are presently being publishedcon cerning recent developments in thyratron transistors. One suchtransistor provides the characteristically large current surge when thebase current is cut off by a triggered bias voltage. It willbeunderstood, of course, that whetherthe double-based diode of Figure 3 isemployed, or whether any one of the several thyratron transistors extantis used, the invention presented by the applicants circuit in Figure 3remains unchanged.

The circuit of Figure 5 is substantially identical with that of Figure 3with the exception that, as in Figure 2, bias resistor 500 is includedin the circuit of solar cell 501 and grid-controlled gas tube 502 isemployed instead of a conventional two-electrode neon tube. Again as inFigure 2, resistor 5.00 is included to supply a bias voltage to thecontrol electrode 503 oftube 502 during the existence of ambient lightto prevent the firing thereof, whereas at night or in the absence ofambient light solar cell 501 is dormant and the bias voltage isremoved.

It should be mentioned that if it is desirable to have two firingsspaced a large time interval apart, then resistors 303 in Figure 3 and504 in Figure 5 may be removed and merely the back-resistance of thedoublebased diode may be employed for a charging path to the associatedcapacitor. .While particular embodiments of the present invention havebeen shown and described, it will be obvious to those skilled in the artthat changes and modifications may be made without departing from thisinvention in its broader aspects, and, therefore, the aim in theappended claims is to cover all such changes and modifications as fallwithin the true spirit and scope of this invention.

I claim:

1. In combination, a storage battery, a solar cell coupled across saidbattery, a transformer having a primary winding and a secondary winding,means intercoupling said battery with said primary winding of saidtransformer and responsive to the voltage exhibited by said battery forgenerating a series of intermittent current surges through said primarywinding, and a gas tube coupled across said secondary winding of saidtransformer.

2. Apparatus according to claim 1 in which said curdiode.

3. Apparatus according to claim 1 in which said curend terminal coupledto said emitter terminal of said rent surge generating means comprises adouble-based diode, and a capacitor coupled between said primarywinddiode having an emitter terminal and first and second ing of saidtransformer and said emitter terminal of said base terminals, said baseterminals being coupled across diode. said battery, a resistor having afirst end terminal cou- 5 pled to said first base terminal of said diodeand a second No references clted-

